Recently, as energy-saving standards, such as “energy star”, continuously appear and upgrade, seven countries and regions (USA, Canada, Japan, Taiwan China, Australia, New Zealand and European Union) in the world have participated an energy star plan proposed by U.S. Environmental Protection Agency.
The energy-saving of the electronic device has been known and accepted by global consumers and becomes a necessary condition for selecting products.
Currently, states of a power supply include several states of S0, S1, S2, S3, S4 and S5, and their descriptions are as follows.
S0: a general operation state in which all devices are turned on.
S1: this state represents that a system is in a low power supplying state in which a CPU is turned off, other device operates normally, and a computer may be woken up by a mouse, a keyboard and the like.
S2: a stand-by state of the power supply which is different from the S1 in that a bus clock is turned off too in the S2.
S3: in this state, all of data stored in memory by an Operating System are maintained and the system enters a “false turned off” state. At this time, power supplied to other devices and apparatuses are cut off, except for the power supplied to the memory for maintaining the data.
S4: the data of the Operating System in the memory is entirely stored into a hard disk, and all of parts stop operate.
S5: a power-off state in which all of the devices are turned off.
Periods of time taken for waking up the computer in S1 to S5 increase sequentially.
The existing adapter comprises both a pulse width modulation unit and an output shaping unit having energy storage elements such as capacitors, inductors, etc. During an operation process of the adapter, these energy storage elements may store some energy and the stored energy can not be sufficiently used to supply power, such that an efficiency of the adapter is low.